Non-aqueous secondary batteries, such as lithium ion secondary batteries, are small and light, high in energy density, and capable of repeated cycles of charge and discharge. For such characteristics, secondary batteries are used in a wide variety of applications. A non-aqueous secondary battery generally includes battery members such as a positive electrode, a negative electrode, and a separator for separating the positive electrode and negative electrode from each other to prevent a short-circuit between them.
Separators that include a substrate made of, for example, polyolefin material such as polyethylene or polypropylene (hereinafter occasionally referred to as a “separator substrate”) and a protection film provided on the substrate for improving heat resistance and puncture resistance have heretofore been used. As the protection layer to be provided on the separator substrate, porous membranes formed of non-conductive particles such as organic or inorganic microparticles bound to one another with a binder have been used (see, e.g., PTL 1).
Recently, in efforts to enhance the performance of non-aqueous secondary batteries, studies have been made to further improve separators having a porous membrane (see, e.g., PTL 2).
Specifically, for example, PTL 2 proposes a separator manufactured by forming on a separator substrate a porous membrane layer containing non-conductive particles and binder and providing on the porous membrane layer an adhesive layer containing a specific particulate polymer. PTL 2 reports that the use of a separator having the adhesive layer on the porous membrane layer allows the separator to be well bonded to the electrode thus improving battery characteristics of a secondary battery.